1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and more specifically relates to an image forming apparatus and an image forming method by which printing is performed upon reading a document.
2. Description of the Related Art
Recently, office networking has been progressing along with digitalization and colorization of documents that are handled. By digitalization, processing and transfer of documents are facilitated and efficiency of work is promoted. In addition, by colorization, documents that are effective and beautiful in appearance are prepared. Given the above, effective intake and output performances in regard to prepared image data are being required of multifunction apparatuses that are installed in offices.
A configuration for input of image data, that is, a configuration of a reading apparatus (scanner, etc.) in a multifunction apparatus is a performance factor that is most intimately related to output image quality in a document image data intake or copying operation. As specific factors, reading speed and reading resolution can be cited.
A reducing optical system is one configuration of a reading apparatus in a multifunction apparatus. Generally, in a high-performance multifunction apparatus, the reducing optical system configuration is adopted in many cases to maintain the reading speed, reading resolution, read image data quality, and other performance factors. In addition, a CCD (Charged Coupled Device) is often the device used in a reducing optical system type reading apparatus.
Also, a contact optical system is another configuration of a reading apparatus in a multifunction apparatus. Generally, in a popular-model multifunction apparatus, the contact optical system configuration is adopted in many cases to maintain the reading speed, the reading resolution, and a read image data quality befitting of a popular-model apparatus, and to keep a unit price low. In addition, due to configuration restrictions, a CIS (Contact Image Sensor) is often the device used in a contact optical system type reading apparatus.
Although as described above, either the reducing optical system configuration or the contact optical system configuration is conventionally adopted as the configuration of the reading apparatus of a multifunction apparatus, what is common to both configurations is that the reading resolution is determined according to the number of pixel sensors positioned along a main scan direction.
Also, the reading resolution, that is, the number of pixel sensors directly influences the unit price of the reading device. That is, to realize high-resolution reading of image data, the reading apparatus must be configured using a device having a large number of pixel sensors, even if the unit price becomes high.
The performance that is demanded of a multifunction apparatus differs according to a usage environment that is applicable. For example, a multifunction apparatus that includes a popular-model-level reading apparatus and a high-performance recording apparatus (printer or other image forming apparatus) may be demanded in an environment where printout from a PC is performed often and a usage rate of a copy function is low.
It is generally known that when a paper document is copied, a copy output image is degraded in comparison to the original document. Also, the image quality of the copy output is strongly dependent on the reading resolution of the reading apparatus and a recording resolution performance of the recording apparatus. That is, if the reading resolution is low, an image quality degradation degree of the copy output becomes high. Obviously, as copying is repeated as child copying, grandchild copying, etc., the image quality degrades further.
A document output method, with which a storage location information of original document data, stored in a database, is embedded in a paper document and, in copying the paper document, the original document data are downloaded based on the storage location information and printed, is described in Japanese Patent Laid-Open No. 2004-364053. By this method, the image quality of the copy output does not degrade and a fixed image quality can be maintained constantly.
In the present Specification, “original document data” refers to image data to be printed that are stored in some storage location (server, etc.) and are the image data to be used as printing data when an image to be printed is read by a reading apparatus and printed.
Furthermore, “super-resolution processing” is being researched as a process for improving the resolution. In super-resolution processing, a plurality of sets of image data that have been read at low resolution are used to significantly improve the inherent resolution of the image data. By using a super-resolution processing art, a plurality of sets of image data read at 300 dpi can be used to form image data with a resolution of 1200 dpi.
FIGS. 18A to 18I illustrate a concept of conventional super-resolution processing. Among these figures, FIG. 18A shows image data to be read by a reading apparatus. A pixel configuration in a case of reading the read image data (FIG. 18A), for example, at 1200 dpi is shown in FIG. 18B. In FIG. 18B, a lattice cell indicated by symbol 1201 indicates pixel data formed at the resolution at which reading was performed (reading resolution). That is, a distance n between pixels corresponds to being a pixel sensor distance when reading was performed at the resolution of 1200 dpi.
A pixel configuration in a case of reading the same image size (the read image data shown in FIG. 18A) at a resolution of 300 dpi is shown in FIG. 18C. As in FIG. 18B, a lattice cell indicated by symbol 1202 indicates pixel data formed at the resolution in which the reading was performed (reading resolution). Thus, on the basis of the distance n between pixels for 1200 dpi, the distance between pixels in the case of reading at 300 dpi is in a direction of being rougher and is 4n.
Because a reproducibility of a read image is proportional to the resolution, a difference of image quality is very clear when the image data read at 1200 dpi (FIG. 18B) and the image data read at 300 dpi (FIG. 18C) are compared as they are.
Super-resolution processing is an art of generating the image data of FIG. 18A from a plurality of sets of image data corresponding to FIG. 18C. By adopting this art, even when the resolution inherent to a reading apparatus is not so high, a read image equivalent to that of a high-resolution device can be formed.
However, adopting the super-resolution processing art needs to meet a certain condition. That is, the certain condition is that the respective low-resolution source images on which the super-resolution processing is to be performed must have a phase shift of less than one pixel in a main scan direction or a subscan direction in-between.
The condition required of super-resolution processing shall now be described using FIG. 18D onward. FIG. 18D is a diagram of the pixel configuration in a case of reading the document image data of FIG. 18A at a resolution of 300 dpi and at the same phase as the document image data. In this figure, because the phase of a reading sensor is matched with the document image, the read image data (FIG. 18E) are the same as the data of FIG. 18D. The read image data, shown in FIG. 18E, make up a first subject image on which the super-resolution processing is performed.
Next, the document image data of FIG. 18A are then read, as shown in FIG. 18F, at a resolution of 300 dpi upon shifting by Δx (Δx<4n) in the main scan direction and by Δy (Δy<4n) in the subscan direction on the basis of the document image data. In this case, the phases of the read image data (FIG. 18G) differ from those of the document image data and are shifted by Δx in the left main scan direction and by Δy in the upper subscan direction in the figure. The read image data, shown in FIG. 18G, make up a second subject image on which the super-resolution processing is performed.
The document image data of FIG. 18A are further read upon shifting just by predetermined phases. That is, as shown in FIG. 18H, the data are read at a resolution of 300 dpi and upon shifting by Δx′ (Δx′<4n, Δx<Δx′) in the main scan direction and by Δy′ (Δy′<4n, Δy<Δy′) in the subscan direction on the basis of the document image data. In this case, the phases of the read image data (FIG. 18I) differ from those of the document image data and are shifted by Δx′ in the left main scan direction and by Δy′ in the upper subscan direction in the figure. The read image data, shown in FIG. 18I, make up a third subject image on which the super-resolution processing is performed.
When the plurality of sets of read data those are low-resolution image data that differ in phase have been obtained, forming into high resolution by the super-resolution processing becomes possible. FIG. 19 illustrates a concept of forming high-resolution image data from the three sets of low-resolution image data. Here, it is shown that by applying the super-resolution processing to the low-resolution image data of FIG. 18E, FIG. 18G, and FIG. 18I that differ in phase, high-resolution image data, such as indicated by symbol 1901, are obtained.
An example of a method of preparing a resolution image from a plurality of low-resolution images that is performed by an image processing apparatus that has acquired the low-resolution images (for example, the read image data shown in FIGS. 18E, 18G, and 18I) shall now be described.
In accordance with a user input indicating acquisition of a high-resolution image from the low-resolution images, the image processing apparatus acquires the read image data shown in FIGS. 18E, 18G, and 18I from the reading apparatus and performs the super-resolution processing based on the acquired three sets of read image data shown in FIGS. 18E, 18G, and 18I.
Among the three sets of read image data shown in FIGS. 18E, 18G, and 18I, there are phase shifts of less than one pixel in the main scan direction and the subscan direction and conversion to high resolution can be performed using these minute shifts. Thus, among the respective pixels that make up the generated super-resolution image (these pixels shall be referred to hereinafter as “generated pixels”), there are pixels that exist neither in the first subject image nor in the second and third subject images. For such a pixel, pixel data, expressing pixel values of pixels existing in a neighborhood of the generated pixel, are used to perform synthesis by a predetermined interpolation process and thereby perform conversion to high resolution. As the interpolation process, an interpolation process by a bilinear method, a bicubic method, or a nearest neighbor method, etc., may be used.
FIG. 20 is a diagram for describing an interpolation process by a conventional, bilinear method.
In FIG. 20, when the interpolation process by the bilinear method is performed, a nearest neighbor pixel 2002, which is the closest in distance from a position of a generated pixel 2001, is extracted from the first subject image and the second and third subject images. Four pixels surrounding the generated pixel position are then determined as neighboring pixels 2002 to 2005 from among the pixels of the subject images (low-resolution images) of FIG. 20, and a data value of the generated pixel is obtained by determining an average of values, with which predetermined weights are applied to the data values of the neighboring pixels, according to the following formula:f(x,y)=[|x1−x|{|y1−y|f(x0,y0)+|y−y0|f(x0,y1)}+|x−x0|{|y1−y|f(x, y0)+|y−y0|f(x1, y1)}]/|x1−x0∥y1−Y0|
By repeating the above process for respective generated pixel positions, the image processing apparatus can obtain high-resolution converted image data, such as indicated by symbol 1901.
In addition, other examples of super-resolution processing by using a plurality of sets of low-resolution image data to generate high-resolution image data that cannot be obtained by the reading apparatus are described in International Patent Publication No. 2004/068862 Pamphlet, Japanese Patent Laid-Open No. 2004-102562, Japanese Patent Laid-Open No. 2004-112644, Japanese Patent Laid-Open No. 2004-151833, Japanese Patent Laid-Open No. 2006-243140, etc.
As mentioned above, when a paper document is copied, the copy output image is degraded in comparison to the original document, and when the reading resolution is low, the image quality degradation degree of the copy output becomes high.
The art disclosed in Japanese Patent Laid-Open No. 2004-364053 is premised on the original document data being stored as electronic data in a database. However, in a case where the original document exists only as a paper document, the image quality of the read image is maintained as that of the original document data and thus if the reading resolution of the reading apparatus is low, the resolution of the original document data may be degraded significantly. That is, in a case where the original document data registered in a server or other storage location are not PDL data or other electronic data but are image data read from the paper document by the reading apparatus, the image quality of the original document data varies according to the resolution of the reading apparatus. In particular, because the image quality of the read image data will be of low image quality if the reading resolution is low as mentioned above, in a case where the reading resolution of the reading apparatus is low, the image quality of the read image data will be low and consequently, the image quality of the original document data will be low.